INHERITANCE OF TRAITS: PEDIGREES

AND GENETIC DISORDERS

Pedigree definition

Pedigree: a family history that shows how a trait is inherited over several generations

Pedigrees are usually used when parents want to know if they are carriers of a particular disorder

Making a Pedigree

Female

Male

Married Couple

Siblings

Filled in symbols indicate individual is affected with a disorder

Example of a Pedigree

You

Parents

Aunts, Uncles Aunts, Uncles

Grandparents Grandparents

Brother

Do any disorders run in this family??

Interpreting a Pedigree

What can you tell from a pedigree?

Whether a family has an autosomal or sex-linked disease or disorder

Autosomal disorder: appears in both sexes equally

Sex-linked disorder: allele is located only on the X or Y chromosome. Most sex-linked genes are on the X chromosome and are recessive

So who would have an X-linked disorder more often, boys or girls?

Whether a disorder is dominant or recessive

Is this disorder 1) autosomal or sex linked, 2) dominant or recessive?

You

Parents

Aunts, Uncles Aunts, Uncles

Grandparents Grandparents

Brother

Autosomal dominant!

Is this disorder 1) autosomal or sex linked, 2) dominant or recessive?

You

Parents

Aunts, Uncles Aunts, Uncles

Grandparents Grandparents

Brother

Sex Linked! (in this case allele is recessive and located on the X chromosome)

Is this disorder 1) autosomal or sex linked, 2) dominant or recessive?

You

Parents

Aunts, Uncles Aunts, Uncles

Grandparents Grandparents

Brother

Autosomal recessive!

Common Genetic Disorders

Color blindness

Sickle cell anemia

Cystic Fibrosis

Hemophilia

Huntington’s Disease

For more info, go to: http://www.ncbi.nlm.nih.gov/pubmedhealth/

Color Blindness

Deficiency to percieve colors

Problem with color-sensing pigments in certain nerve cells of the eye

About 1 in 10 men have some form of color blindness.

Sex-linked disorder

Sickle Cell Anemia Disorder where abnormal

hemoglobin (a protein inside red blood cells) is produced and warps red blood cells

Sickle cells deliver less oxygen to body’s tissues and can get stuck in small blood vessels

Recessive trait, tends to be seen in people of African or Mediterranean descent

Cystic Fibrosis Recessive, autosomal disease

Life threatening, causes thick mucus to build up in various areas of the body (lungs, digestive tract, etc).

Tends to run in Caucasians, of Northern/Central European descent

(1 in 29 Americans

carry the allele)

Average life span in US

for people with CF is 37,

death usually caused by

lung complications

Hemophilia Bleeding disorder, where it takes a long time for blood to clot (body lacks proteins involved in clotting)

Sex-linked

(carried on the X

chromosome)

Treatment

involves

injection with

missing clotting

protein

Huntington’s Disease

Autosomal, dominant

Deterioration of brain tissue, usually begins between age 30 and 40.

No cure, but have medications to cope with symptoms

People usually die 15-20 years after onset of

degeneration